Motor ground

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Twophase

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I've noticed many schematics don't show a ground going to a motor from a controller (the only conductors between the controller and motor are power conductors) and show the motor grounded directly (to the physical ground or a metal frame). Is this code complaint?

I'm still trying to get a grasp of grounding, as it is one of the most misunderstood sections of the NEC
 
You need an EGC along with the circuit wiring to the motor. If a flexible wiring method is used to prevent the transmission of vibration it must be a wire type EGC.
 
The schematic is illustrating how the motor controller works, not how to wire to code. The ground symbol drawn at the motor is just shorthand. You would need a proper equipment grounding conductor from the source of the power to the motor to be code compliant.
 
In my scenario, my motor doesn't have ground lugs on the load side....so could I take credit for having the controller and motor both grounded to a common frame?
 
I am using IMC, so it is metallic. When would I be able to take credit for that? That can really help especially when there are conduit fill issues
 
ActionDave said:
The entire run of IMC counts as an EGC. Usually hooking up a motor means transitioning to some kind of flex conduit and there are limitations on that. Look at 250.118
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Correct. We were planning on using a little bit of LFMC at the end to reduce vibration
 
Twophase said:
Correct. We were planning on using a little bit of LFMC at the end to reduce vibration
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As stated in post #2 then you'll need a wire type EGC in the LFMC even if the LFMC qualifies as an EGC according to 250.118.
 
Just to clarify what's already been mentioned, you need a wire-type EGC within the LFMC. But the IMC can be used by itself without an internal wire for the EGC that would exacerbate the conduit fill issue in your other post. If you transition between the IMC and LFMC with a suitable box, then you can connect the short section of wire-type EGC for the LFMC to a bonding bushing on the end of the IMC in the box.
 
Twophase said:
Correct. We were planning on using a little bit of LFMC at the end to reduce vibration
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Probably not for vibration, but for ease of connection. If you have motor vibration thats bad. For the LTFMC get connectors with an external bonding lug (T&B makes) run the EGC on the outside of the flex, limit 6 ft. At the motor end, use a bonding bushing in the junction box with a bonding jumper to the bonding terminal in the motor j box (sometimes there are reducing washers in the motor junction box)
 
Twophase said:
I've noticed many schematics don't show a ground going to a motor from a controller (the only conductors between the controller and motor are power conductors) and show the motor grounded directly (to the physical ground or a metal frame). Is this code complaint?

I'm still trying to get a grasp of grounding, as it is one of the most misunderstood sections of the NEC
Click to expand...
Grounding is misunderstood as tend to use the term ground for when it is not a ground. What you are discussing is an EGC.
Look up the definition of ground.
Recommend you get the Mike Holt text and DVD on Grounding and Bonding. Then you will get it.
 
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